1. Field of the Invention
The present invention relates generally to hydrogen gas generating systems and, more particularly, to a system for the generation of hydrogen gas resulting from the reaction of molten lithium or lithium alloy fuel with water in a contained vessel.
2. Discussion of the Prior Art
The hydrogen gas generator reactor of the present invention is one of the key energy producing components of a Rankine cycle vapor pressure or steam engine, for example, which obtains its driving heat energy from a chemical reaction other than the usual combustion of fuel with oxygen from the air. The theoretical possibility of utilizing the reaction energy of a reactive metal fuel such as aluminum, magnesium or lithium and alloys or hydrides of these and similar reactants, with an "oxidizer" such as hydrogen peroxide, Freons, sulfur hexaflouride, water and others, has been recognized for many years. However, the technical difficulties and conflicts standing between a theoretical construction of such a power system and a practical apparatus which is functional outside of the laboratory are legion.
By way of example, many of the fuel-reactant combinations proposed in the past have required that the fuel be raised above ordinary ambient temperatures in order to permit reaction with the reactant. Such a heating requirement necessitates that some heating means, such as electrical heating coils or pyrotechnic chemicals be provided. In the former case, a significant start-up delay is incurred while a portion or all of the fuel is raised to reaction temperature. In the latter case, the pyrotechnic chemicals, which are or may be considered to be low velocity explosives, present the possibility of damaging the interior of the reaction chamber and escape of highly reactive or toxic fuels. Such pyrotechnic heating chemicals also frequently produce a quantity of gaseous reaction products which must be contained within the reaction chamber, or else vented therefrom while preventing loss of fuel.
Another undesirable aspect of many previously proposed fuel-reactant systems is that intermediate reaction products or end reaction products are formed which on the one hand inhibit further progress of the reaction between the fuel and reactant or, on the other hand, freeze at a temperature higher than the desired reaction chamber temperature. In the one case, complex structures and methods have been proposed to cure the shortcoming by removing the intermediate or final reaction product from the reaction chamber. Alternatively, only a portion of the fuel could be brought into contact with the reactant so that reaction products could not contaminate the remaining fuel. Again, complexity is increased.
The problem of the reaction intermediates or final products freezing at too high a temperature presents the difficulty that the reaction chamber may soon become filled with a "slush" of frozen reaction products in a slurry of molten fuel. Similarly, the high-freezing constituents present in the reaction chamber may form a "frost" or crust on the coolest surfaces present. These cool surfaces will ordinarily be heat transfer surfaces where it is desired to transfer heat from the chemical reaction for utilization in a steam or vapor pressure Rankine cycle engine. Such a crust on the heat transfer surfaces will ordinarily have a relatively high insulation value in comparison with the molten fuel. As a result, the crusted reaction products themselves progressively inhibit heat transfer from the reaction chamber to the engine.
One approach aimed at solving the problem just mentioned is disclosed in U.S. Pat. No. 4,698,974 to Wood. In the Wood disclosure, a fuel is reacted with water in the absence of oxygen gas to produce heat and hydrogen gas. The heat from this reaction is sued to produce water steam. The hydrogen gas is burned with oxygen gas in a separate second reaction chamber to produce super heated steam. The steam from the first reaction chamber is used as a coolant and diluent in the second reaction chamber so that steam flowing from the second reaction chamber to a turbine, or other expander, has a metallurgically acceptable temperature.
A shortcoming of the Wood invention, however, is that a hydrogen gas bearing reaction intermediate is formed which initially partially prevents the evolution of the hydrogen gas from the first reaction chamber. As the reaction progresses, the reaction intermediate further reacts to release the bound hydrogen. The result is that over the period of the reaction, the rate of hydrogen gas production is at first relatively low, reaches a stable plateau, and then raises above the plateau as the fuel supply is consumed.
A consequence of this nonuniform rate of hydrogen gas production is that the power output of the Rankine cycle steam engine is relatively low initially and cannot be increased until the hydrogen gas production rate of the chemical reaction chamber increases. Understandably, this sluggish initial power output of such a system is undesirable in almost every prospective application. Additionally, the nonuniform rate of hydrogen gas production creates many difficulties in controlling the power output level of the Rankine cycle engine.
An improvement on the Wood system is presented in U.S. Pat. Nos. 4,643,166 and 4,730,601 to Hubele et al which, according to one aspect, provides a two-part fuel composition including a first or main fuel part of magnesium and aluminum in a molar ratio of 1:2, respectively. The second or starter fuel part is composed of lithium hydride, magnesium and aluminum in equal molar ratio. On a weight basis, the starting fuel composition and main fuel composition are presented at a ratio of about 1:4. In the reaction chamber, the above-outlined fuel is present in the form of prealloyed powders produced, for example, from condensed vaporized or atomized metal. The reaction chamber structure provides in addition to heat transfer means, a means for introducing water into the chamber for reaction with the fuel.
In one embodiment, the means for introducing water comprises a manifold with foraminous distribution tubes depending in the fuel. The distribution tubes are immediately surrounded by a comparatively thin layer of the starting fuel part. The main fuel part is received within the reaction chamber around the distribution tubes and layer of starting fuel part.
In another embodiment, the main fuel part is disposed in a lower portion of the reaction chamber. In an upper portion of the reaction chamber is disposed an appropriate quantity of the starting fuel part and, in this instance, the reaction chamber includes a water inlet nozzle disposed in an upper part of the reaction chamber above both the starting and main fuel parts. Preferably, the water nozzle is separated from the fuel during operation of the reaction chamber and engine.
A primary advantage of the patented system as mentioned therein is the stated absence of any need or requirement to provide fuel preheating before the reaction chamber is operational. According to a further stated advantage, the introduction of simple water is all that is required to initiate operation of the reaction chamber to produce both heat and a supply of hydrogen. This latter feature is said to be of particular advantage when the invention is sued in connection with a water borne vehicle.
However, the Hubele et al. invention exhibits a number of drawbacks. Specifically, the disclosures in the Hubele et al. patents relate the use of two separate and distinct fuels and, furthermore, do not require that the fuels be raised in temperature to a molten mass as does the present invention. Indeed, those patents stress the desirability of a reaction which is performed at common ambient temperatures and which do not require preheating or pyrotechnic chemicals to be used in starting the reaction. While the Hubele et al. patents imply that there is a strategic advantage to starting at room temperature and to reacting a starting charge first and, subsequently, the main fuel, they also state that the entire fuel mass will melt in very short order. In effect, what will occur is that the operator of the Hubele et al. system will not be able to control the local reaction to first use the start charge with the result that a molten mass will be achieved with only one fuel, not two, and the stated claim of a regulated, flat, hydrogen gas production will not be achieved.
Other patents of interest include U.S. Pat. No. 3,353,349 to Percival and U.S. Pat. No. 5,117,635 to Blau. Percival discloses a closed cycle thermal engine provided with a combustion system for heating the working gas thereof. The combustion system produces nongaseous byproducts and operates at substantially constant volume by employing molten lithium or sodium as a fuel and certain gaseous nonhydrogen containing Freon-type fluorocarbon compounds as the oxidizer. Blau describes an open-cycle Rankine steam engine. One of the energy-producing components of the engine does utilize molten lithium as a fuel. However, hydrogen gas is not generated anywhere within the system.